The present invention relates to electrode assemblies for use in electrolytic cells. More particularly, the invention relates to electrode assemblies for use as cathodes in the electrolytic refining or electrowinning of metals, such as copper, or in the manufacture of chlorates, perchlorates, manganese dioxide, hydrogen, fluorine, or permanganate.
In the electrolytic refining of copper, impure copper which is formed into slabs directly from the crude metal as it is obtained from copper ore is utilized. These slabs are used as the anode in an electrolytic cell. Often, a sheet of pure copper is used as the cathode, but stainless steel may also be used. The electrolyte is generally a dilute solution of a salt of Cu.sup.2+. As electricity passes through the cell, copper is oxidized to Cu.sup.2+ at the impure copper anode, and Cu.sup.2+ is reduced to metallic copper at the pure copper or stainless steel cathode, which may be coated with a thin layer of graphite so that the fresh copper deposit can be easily removed. As the impure metal slab anode dissolves, any metals that are harder to oxidize than copper will not dissolve, but will drop into a sludge in the bottom of the cell, from which they can be recovered. Metals that are easier to oxidize than copper will dissolve into the electrolyte, but will not plate out at the cathode. Copper produced by this method generally has a purity of about 99.95 percent.
The use of a pure copper sheet as the cathode has a number of disadvantages. Exposure of portions of the copper plate to air in the vicinity of the electrolyte can result in corrosion of the copper sheet. Moreover, the copper sheet must be supported above the electrolyte, and must be connected to a voltage source. Both of these functions are typically carried out by suspending the sheet below a hanger bar. When the hanger bar is made of copper, a high electrical conductivity is obtained, and the copper plate is easily attached to the hanger bar. However, the copper hanger assembly is susceptible to corrosion, and has a relatively low tensile strength. As the process proceeds, the cathode sheet grows heavier, while at the same time the tensile strength of the copper in the hanger bar may decrease due to heating and softening of the copper.
Coating or jacketing the copper hanger bar with a corrosion resistant metal, such as stainless steel, presents a number of other difficulties. Attachment of the copper sheet to the jacketing metal in a way that provides sufficient support for the sheet and sufficient electrical contact between the sheet and the coating or jacketing is often difficult. Moreover, preparing the coated or jacketed hanger assembly is difficult and expensive, and existing methods may allow electrolyte to leak inside the jacket, corroding the inner copper bar, or may result in unacceptably high contact resistance between the inner core and the metal jacket. This is of particular concern where the jacketing metal has an electrical conductivity lower than that of the core metal.
U.S. Pat. No. 4,647,358 to Bartsch et al. discloses a cathode in FIGS. 4, 6, and 7 that comprises a plate 1 welded to a sheath 2 tightly surrounding a hollow copper bar 3. The plate and the sheath may be formed of stainless steel. The oval shape of the copper bar and sheath shown in FIG. 4 results from deforming a copper bar and sheath of circular cross section, as shown in FIG. 3. Reference characters 5, 6, and 7 in FIG. 4 identify welds.
U.S. Pat. No. 4,871,436 to den Hartog discloses a hanger bar for an electrode. As shown in the drawings, an electrode plate 6 is suspended from a hanger bar 1 formed from a copper sheath 8 drawn over steel and copper core elements 9 and 10, respectively. In the finished hanger bar, copper core elements are located at the ends of the hanger bar, and the steel core element is disposed between them.
U.S. Pat. No. 4,882,027, to Borst et al., discloses an electrode, shown in FIGS. 1-3, made up of stainless steel plate 16 with lugs 18, 20 at its top edge welded to copper cladding 14 about steel or iron bar 12.
U.S. Pat. No. 3,260,662, to Henegar, discloses an anode designed for use in an electrolytic alkali-chlorine cell. As shown in FIG. 1, the lead-in 21A of a brass pipe is pressed into the thick-wall portion 12A of a titanium sleeve embedded in graphite anode 14A.
U.S. Pat. No. 2,434,731, to Eltz, U.S. Pat. No. 3,515,661, to Coulter et al., and U.S. Pat. No. 4,606,804, to Schulke et al., disclose further examples of plate-type electrodes designed for use in electrolytic cells.